Mt Ijen is 2443 metres above sea level. Three major eruptions 3500 years ago created a caldera measuring 22 by 25 kilometres. The volcano is world-famous for its crater lake with the most acidic water in the globe.
This lake is over 182 metres deep and has 32 million cubic metres of beautiful turquoise green water. The crater rim embraces the lake, its lower area measures 960 by 600 metres. Higher up, it measures 1600 by 1160.
It lies within the Ijen Nature Reserve, Banyuwangi province, East Java. Every night, between 2.00am to 4.00am, blue fire appears in the crater - the reason for Mt Ijen's fame. You can see this phenomenon in only two places in the world - in Iceland, and in Ijen.
From the Ijen caldera, you can also see the group of stratovolanoes which includes Gunung Merapi, Gunung Raung, Gunung Suket, Gunung Rante and many other post-caldera cones and craters.